Technologies have been developed that uses a unique ID of a communication apparatus, such as a calling number of a portable telephone, for user authentication. For example, Patent Document 1 discloses a technology that a service system for providing services to a user stores therein a user ID and a calling number of a portable telephone in an associated manner as a user ID matching list, and that determines that the user is an authorized user, when a user ID and a calling number are acquired from a user terminal and a portable telephone, respectively, and a pair of the user ID and the calling number thus acquired has been stored in the user ID list.
Patent Document 1: Japanese Patent No. 3497799